Intermittent starting problems (Mazda5)

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BMW M3 / Mazda5
Been having an issue where, every once in a while, it'll take a lot more cranks than usual to start.

Then, in the past couple of days, I've noticed it will sometimes fire up and then immediately die – but if I retry immediately, key to Acc or Off and then back to Start, it fires right up with no issue.

Both scenarios seem to occur on warm starts, e.g. when the car has been sitting for like 1-2 hours. Haven't seen it happen on a cold or hot start.

No CEL so far. The car used to stumble very slightly on heavy throttle applications, esp. in the upper half of the rev range, but that seems to have stopped on its own. There's a very mild vibration in the cabin at idle. Other than that, the engine revs and pulls smoothly and returns good fuel economy (21-25 mpg in mixed use, including lots of stop-and-go and some lead-footed driving).

Thoughts on what to check? Anyone else had these issues?
 
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2008 Mazda5 GT
Always park in a (every so slight) decline and bump-start car? Isn't this why you got a manual :D


IIRC, the Mz3 had issues with the ground or positive cable to the starter. Check connection points and trace wire.

I'm fortunate to say I've not had many issue with starting the car, except 'one' time the starter wouldn't turn. Got under and gave it a strong whack with hammer (again piece of wood, not direct metal to metal) and its been behaving since.
 
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2008 Mazda5 GT
Been having an issue where, every once in a while, it'll take a lot more cranks than usual to start.

Then, in the past couple of days, I've noticed it will sometimes fire up and then immediately die – but if I retry immediately, key to Acc or Off and then back to Start, it fires right up with no issue.

Both scenarios seem to occur on warm starts, e.g. when the car has been sitting for like 1-2 hours. Haven't seen it happen on a cold or hot start.

No CEL so far. The car used to stumble very slightly on heavy throttle applications, esp. in the upper half of the rev range, but that seems to have stopped on its own. There's a very mild vibration in the cabin at idle. Other than that, the engine revs and pulls smoothly and returns good fuel economy (21-25 mpg in mixed use, including lots of stop-and-go and some lead-footed driving).

Thoughts on what to check? Anyone else had these issues?
Re-reading this, I don't think it's the starter.
-If it takes more cranks than usual to start, then the starter is turning. A bad starter would not turn. A long crank is typically indicative of a failing battery (battery's CCA degrade).
-Since it did fire up, the starter is out of the equation of it dying. Something on the electrical (or air/fuel since combustion is simply air, spark, fuel) is causing it to die.

What is the condition/age of the battery?
Check/Clean electrical ground of the main harness to/from battery and starter?
If not done so, clean throttle body and reset PCM and go through idle-learn process.
example guide: Mazda throttle body relearn
 
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BMW M3 / Mazda5
Re-reading this, I don't think it's the starter.
-If it takes more cranks than usual to start, then the starter is turning. A bad starter would not turn. A long crank is typically indicative of a failing battery (battery's CCA degrade).
-Since it did fire up, the starter is out of the equation of it dying. Something on the electrical (or air/fuel since combustion is simply air, spark, fuel) is causing it to die.
Agreed.

What is the condition/age of the battery?
About 4 years old. My stereo installer said it was slow-cranking after 1-2 hrs of having the dome lights on, though they might just have seen the same issues I describe here and misinterpreted them. Either way, I'll probably replace the battery whenever my preferred vendor gets them back in stock.


Check/Clean electrical ground of the main harness to/from battery and starter?
If not done so, clean throttle body and reset PCM and go through idle-learn process.
example guide: Mazda throttle body relearn
Nice. Thanks.
 
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2010 Mazda 5 Sport
Usually a slow start with no code can be a few things:

Fuel pump going bad. Not enough fuel pressure.
Cam\Crank Sensors are going bad. Timing can't be detected by ECU.
MAF going bad\dirty. ECU can't determine the correct fuel mixture.

Basically, when cranking, the ECU is looking at those inputs and deciding whether to energize the coils. If they are wonky, the ECU won't fire things up.

There may be more things to check, but I'd start with those.

Like was said, checking grounds is never a bad thing either.
 
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Mazda5 2015 GS
Have something similar happening sometimes.
Usual trigger is moving my car in the street then shutting it off immediately.
Next start a few hours later will be difficult. Even managed to flood it last time it happened.

Starter is usuallu reacting as expected, few misfires heard on 1st attempt, then starts right up on the 2nd one most of the times.

My workaround for now is to drive a bit around the block or idling instead of turning it off too soon. No way I'm paying diag fee at the dealer to hear again they can't duplicate the issue.
 
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2015 Mazda 5 Sport
If the ground wires to the engine and the starter are not the issue (inspect with resistance reading, not just visual), check the battery model and have AAA or auto zone check the expected battery spec. Wrong type of battery can cause starting issue but engine dying right after it started suggested an additional issue.

Possible faulty engine mount.

> Next start a few hours later will be difficult. Even managed to flood it last time it happened.

If the hard starting only appears shortly after it has been shut off, it could be a faulty coolant temperature sensor that flooded the warm engine with gasoline:
 
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BMW M3 / Mazda5
Been thinking about this a bit more. If it were a fuel pump issue, wouldn't it show up on cold starts as well?

To recap:

- Cold start: Fires right up
- Warm start (sitting for 1-2 hours): Hard start, often stalls – UNLESS I turn the key on and then off before starting, in which case it fires right up
- Hot start (sitting for 5-10 mins): Fires right up

:unsure:
 
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2008 Mazda5 GT
- Warm start (sitting for 1-2 hours): Hard start, often stalls – UNLESS I turn the key on and then off before starting, in which case it fires right up
6419838_sd.jpg

Suckers are hard to find...

Can you try this warm start; turn the key to 'on' position and wait 3 seconds (instead going back to off), then restart -does it start?
 
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2010 Mazda 5 Sport
Turning the key on and off can "bump" the fuel pump to get to working and build up pressure. You're cycling power to the fuel pump and it just gets it to work. Eventually you will have to do it a few times and then it won't work at all.

Fuel pumps are funny. When they start going out, they can work fine or not at random times. Cold starts can be easy, and when the pump gets hot, it doesn't work well. Sometimes the other way.
 
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BMW M3 / Mazda5
Turning the key on and off can "bump" the fuel pump to get to working and build up pressure. You're cycling power to the fuel pump and it just gets it to work. Eventually you will have to do it a few times and then it won't work at all.

Fuel pumps are funny. When they start going out, they can work fine or not at random times. Cold starts can be easy, and when the pump gets hot, it doesn't work well. Sometimes the other way.
Got it.

So let's say the fuel pump is the culprit. Will that necessarily show in a fuel pressure test?
 
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2010 Mazda 5 Sport
It can. But won't rule it out either since you're chasing a weak pump and not a dead one. Could be a fuel regulator going bad too.


Hard starts can be a pain to find. Might ultimately not be a fuel issue. Like was mentioned above, it might be a coolant temp sensor or something.
 
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BMW M3 / Mazda5
Can you try this warm start; turn the key to 'on' position and wait 3 seconds (instead going back to off), then restart -does it start?
Got a chance to try this. Didn't work.

Still fires right up on cold starts and hot starts. Only warm starts require the on-off-start sequence, which always works.
 
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2008 Mazda5 GT
Got a chance to try this. Didn't work.

Still fires right up on cold starts and hot starts. Only warm starts require the on-off-start sequence, which always works.
When you waited for the ~3sec, did you hear the fuel pump prime (it is faint but audible in driver seat, pump is under rear passenger seat). Next I'd try to a warm start (again after 3-5 sec wait) with the gas pedal pressed down.

These warm starts, can I assume the key was removed from the ignition and out of immobilizer range?

I'm still leaning toward electrical issue, perhaps ground around the starter. Disconnect battery and starter, and wire brush all connections.
 
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BMW M3 / Mazda5
When you waited for the ~3sec, did you hear the fuel pump prime (it is faint but audible in driver seat, pump is under rear passenger seat).
I don't think I've ever heard it prime, TBH – including on cold and hot starts when it fires right up...

Next I'd try to a warm start (again after 3-5 sec wait) with the gas pedal pressed down.
Roger that.

These warm starts, can I assume the key was removed from the ignition and out of immobilizer range?
Yes. No comfort access in this car, either.


I'm still leaning toward electrical issue, perhaps ground around the starter. Disconnect battery and starter, and wire brush all connections.
Will do when I replace the battery, which will likely be soonish.
 
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2008 Mazda5 GT
This worked! It took more cranks and stumbled, but it didn't stall.

EDIT: Starting with the gas pedal pressed, but without the 3-5 sec wait, also worked. Same results.
If this is 100% reproducible, I'd take out the (FoMoCo) throttle body, clean it thoroughly, and go through idle relearn.